Conventional storage devices consist of a box wherein multiple types of units can be inserted. It is possible to set up a stopper in this kind of box that allows the insertion of certain types of units, and hinders the insertion of other types of units. A device for preventing improper insertion is recited in Japanese Laid-open Patent Publication No. 2003-281850.
Changing the type of unit for which insertion is to be prevented is possible by changing the position of the stopper in relation to the box. However, if the stopper is placed in the wrong position, it is possible that units for which insertion should not be prevented will in fact have their insertion prevented. In this way, there is a risk of setting up the device so that insertion prevention targets the wrong units.